1. Field of the Invention
This invention relates to an interface between digital Josephson junction circuitry and digital semiconductor signal processing circuits. In particular, it relates to a superconducting digital logic amplifier to provide a voltage gain to allow Josephson digital circuit signals to be fed into widely available semiconductor digital circuits.
2. Description of the Related Art
Josephson junctions are, of course, well known in the art. U.S. Pat. Nos. 4,432,134 issued Feb. 21, 1984, to Jones et al.; 4,242,419 issued Dec. 30, 1980, to Dayem et al.; 4,202,959 issued Sept. 2, 1980, to Kroger; and, 3,816,845 issued June 11, 1974, to Cuomo et al., give examples of Josephson junction configurations and processes for making them.
Circuitry using Josephson junction is shown in U.S. Pat. No. 3,458,735 issued July 29, 1969, to Fiske. Fiske teaches the use of individual electromagnetic control means to obtain a voltage output, where the voltage output is the sum of the individual control voltage. In a paper entitled "A Josephson Counter-Circuit with Two-Phase Power Supply" by Nakagawa et al. (Abstracts of the 17th Conference on Solid State Devices and Materials, Tokyo, 1985, pp. 123-126), a Josephson digital circuit is described which utilizes Josephson junctions to provide a data-latch function for a counter-circuit.
Recent advances in superconductivity may lead to widespread use of superconductor circuits in radar signal processing. The picosecond switching speed of Josephson junctions could be applied in an analog-to-digital converter capable of operation at X-band frequencies. High-speed shift registers are under development, which could be used to store the output of such an A/D convertor. A 10 GHz shift register could also be used to multiplex or demultiplex a fast data stream. While most development has been in the traditional metallic superconductors which operate at liquid helium temperature (4.degree. Kelvin), this technology will generally be applicable to the new high temperature ceramic superconductors.